Abrasive compounds for semiconductor planarization

ABSTRACT

A polishing slurry for semiconductor planarization containing cerium oxide particles and water, wherein the content of the cerium oxide particles having a diameter of 3 μm or more is 500 ppm or less (weight ratio) in a solid, preferably 100 ppm or less and it is more preferable that D99 (99% by volume of the whole particles in polishing slurry) of the cerium oxide particles is 1 μm or less. The polishing slurry can reduce the generation of scratches, and can polish a surface of the semiconductor substrate in the wiring formation process of semiconductor device precisely at a high speed.

TECHNICAL FIELD

The present invention relates to a polishing slurry, and particularlyrelates to polishing slurries for semiconductor planarization.

BACKGROUND ART

A precise polish process for polishing the surface of a material isrequired in, for example, optical disk substrates, a magnetic disks,glass substrates for flat panel displays, clock boards, camera lenses,glass material used for various lenses and crystal material for filtersor the like for optical components, substrates of a silicon wafer or thelike for semiconductors, and insulated films, metal layers and barrierlayers or the like formed in each process for manufacturingsemiconductor devices. The surfaces of these materials require highaccuracy polishing. Therefore, for example, polishing agents have beengenerally used, using silica, zirconium oxide and alumina or the likealone or in combination of two or more kinds as polish particles.Referring to a form of the polishing agent, for example, a slurry-likepolishing agent obtained by dispersing the polish particles in a fluid,a polishing agent obtained by curing the polish particles with a resinand other binder, and a polishing agent obtained by adhering and/orfixing only particulates of the polish particles on the substratesurface of fiber, resin and metal or the like with the binder have beengenerally used.

A silica polishing slurry using particularly silica particulates as thepolish particles has been widely used as the polishing slurry forprecision polish for a wiring formation or the like in the manufactureof a semiconductor integrated circuit (hereinafter, referred tosemiconductor) because of little scratch generation of a surface to bepolished. However, since the polishing speed of the silica polishingslurry is slow, attentions have been recently focused on a cerium oxidepolishing slurry containing cerium oxide having a fast polishing speed(for example, see Japanese Patent Application Laid-Open Nos. 2000-26840and 2-371267). However, the cerium oxide polishing slurry has a problemof generating more scratches as compared with the silica polishingslurry.

Though the cerium oxide polishing slurry has been used for glass polishfor many years, it has been necessary to avoid impurity contamination asmuch as possible so as to apply the cerium oxide polishing slurry to theplanarization of the semiconductor. Then, rare earth materials arerefined once, and a high purity cerium oxide is obtained via a ceriumsalt. As the cerium salt, cerium carbonate, cerium oxalate and ceriumnitrate or the like are used. The polishing slurry for semiconductorplanarization has been manufactured by dispersing the cerium oxideobtained by calcining and grinding these cerium salts.

Though it has been presumed that the scratches generated in the polishprocess relate to the particle diameter of the polishing slurry,quantitive evaluation results have been seldom obtained. It has beensaid that the scratches are decreased when a filter in the manufacturingprocess is used and coarse particles are removed in the case of thesilica polishing slurry. In this case, the relationship between thephysical properties of the polishing slurry after filtration and thescratches is not apparent.

Though it has been considered that the cerium oxide polishing slurry hasa larger mean particle diameter than that of the silica polishing slurryand has a great content of the coarse particles, since a measurementtechnique having high sensitivity has not been established, thereliability of the measurement results has been inadequate. Therefore,the relationship between the coarse particles and the scratches ismerely conceptually understood, and an effective specific measure hasbeen deficient.

For example, in a paragraph (0020) of Japanese Patent ApplicationLaid-Open No. 10-154673, the maximum particle diameter is measured by alaser diffraction type particle size distribution meter, and JapanesePatent Application Laid-Open No. 10-154673 discloses that one having 1μm or more is not contained. Thus, the scratches have been prevented byconventionally measuring using a laser diffraction type particle sizedistribution meter of Mastersizer (trade name, manufactured by MalvernInstruments Ltd.) or the like to reduce the maximum particle diameter ofthe particle.

However, even if the maximum particle diameter detected by the particlesize distribution meter is reduced, the prevention of the scratches islimited, so that responding to integration of the semiconductor thesedays has been difficult.

Consequently, the present inventor has conducted earnest studies of thecause. As a result, the present inventor found that, in fact, particlesof 3 μm or more considered not to exist in the measuring method usingthe particle size distribution meter exist in a very small quantitywhich is undetectable, and affect the scratches.

On the other hand, high integration of the semiconductor has beenadvanced, and processing size of wiring or the like is miniaturized to100 nm. As the processing has been miniaturized, the defective reductionof the scratches or the like has been still strongly required, and thepolishing slurry satisfying all of the polishing speed, planarizationand scratch reduction has been required.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a polishing slurryfor semiconductor planarization capable of maintaining a suitablepolishing speed, reducing the generation of the scratches and preciselypolishing the surface of the semiconductor.

The present inventor has conducted earnest studies of the reduction ofthe scratches due to the polishing slurry for semiconductorplanarization. As a result, the present inventor found that thescratches can be decreased by removing the coarse particles contained ina small amount in the polishing slurry, thereby the present inventionwas accomplished.

A polishing slurry for semiconductor planarization of the presentinvention, containing cerium oxide particles and water, wherein thecontent of the cerium oxide particles having a diameter of 3 μm or moreis 500 ppm or less in a solid.

Furthermore, it is preferable that the polishing slurry contains adispersing agent.

Furthermore, it is preferable that the particle diameter is 1 μm or lessin 99% by volume of the whole cerium oxide particles.

A surface of a semiconductor can be polished at a high speed in a wiringformation process by the present invention. Also, the surface of thesemiconductor has good flatness, and scratches can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an example of the surface magnified photograph of a film (onelayer) type filter for analysis punched by laser machining used formeasuring the content of coarse particles in an Example of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the embodiment of the present invention will be describedin detail.

The polishing slurry for semiconductor planarization of the presentinvention (hereinafter, referred to as polishing slurry) contains thecerium oxide particles and the water.

As a cerium oxide polishing slurry used for polishing a silicon oxidefilm formed by a TEOS-CVD method or the like has a larger primaryparticle diameter, and has little crystal distortion, that is, goodcrystallinity, high-speed polishing can be performed. However, thesilicon oxide film tends to have polishing scratches thereby. Therefore,it is preferable that the average value of the primary particle diameterof the cerium oxide used in the present invention is within the range of5 nm to 300 nm while the cerium oxide particles do not limit themanufacturing method. Herein, “primary particle” means a particleequivalent to a crystallite surrounded by boundaries, measured andobserved by SEM (scanning electron microscope).

Since the cerium oxide particles manufactured by the above method areeasily flocculated, it is preferable that the cerium oxide particles aremechanically grinded. Preferable examples of grinding methods include adry grinding method using a jet mill or the like, and a wet grindingmethod using a planet bead mill or the like. The jet mill is describedin, for example, Chemical Industrial Paper Collection (Kagaku KougyouRonbunshu), vol. 6, No. 5 (1980), 527-532.

It is preferable that the polishing slurry of the present invention is acomposition containing the cerium oxide particles, a dispersing agentand water. For example, the polishing slurry is obtained by dispersingthe composition containing the cerium oxide particles produced by theabove method and the dispersing agent in the water.

Though the concentration of the cerium oxide particles is not limited,the concentration is preferably within the range of 0.5% to 20% byweight, more preferably 1% to 10% by weight, and still more preferably1.5% to 5% by weight in view of easiness for handling the polishingslurry in the form of a liquid dispersion.

The dispersing agent is preferably a polymer dispersing agentcontaining, for example, an acrylic acid ammonium salt as acopolymerization component since it is preferable to suppress thecontent of alkaline metals such as sodium ion and potassium ion, halogenand sulfur to 10 ppm or less in view of the use for polishing asemiconductor device.

The addition amount of the dispersing agent is preferably within therange of 0.01 parts to 5.0 parts by weight based on the cerium oxideparticle of 100 parts by weight in view of the dispersibility andprevention of sedimentation of the particles in the polishing slurry,and the relationship between the polishing scratch and the additionamount of the dispersing agent.

The weight-average molecular weight of the dispersing agent ispreferably within the range of 100 to 50,000, and more preferably 1,000to 10,000. When the molecular weight of the dispersing agent is lessthan 100, sufficient polish speed is hardly obtained at the time ofpolishing the silicon oxide film or a silicon nitride film. When themolecular weight of the dispersing agent exceeds 50,000, the dispersingagent has high viscosity, and the preservation stability of thepolishing slurry tends to be descended. In the present invention, theweight-average molecular weight is a value measured by gel-permeationchromatography and expressed in terms of standard polystyrene.

As a method for dispersing the cerium oxide particles in water, ahomogenizer, an ultrasonic disperser and a wet ball mill or the like canbe used in addition to a dispersing processing using a usual stirrer.

Since the secondary particle diameter of the cerium oxide particles inthe polishing slurry of the present invention produced thus has aparticle size distribution, it is preferable that the secondary particlediameter is 1.0 μm or less in 99% by volume (hereinafter, referred toD99) of the whole cerium oxide particles. If D99 exceeds 1.0 μm, thegeneration of the scratches is increased.

It is preferable that the median (hereinafter, referred to D50) of thesecondary particle diameters of the cerium oxide particle is within therange of 0.03 to 0.5 μm, and more preferably 0.05 to 0.3 μm. When themedian of the secondary particle diameters is less than 0.03 μm, thepolish speed tends to be reduced. When the median exceeds 0.5 μm, thepolishing scratches are easily generated on the surface of a film to bepolished. The median (D50) and the D99 of the secondary particlediameters of the cerium oxide particles in the polishing slurry can bemeasured by a light scattering method, for example, a particle sizedistribution meter (for example, manufactured by Malvern InstrumentsLtd., trade name: Mastersizer Microplus).

The content of coarse particles having a diameter of 3 μm or moreoccupied in the whole solid in the polishing slurry are preferably low.The coarse particle of 3 μm or more means a particle captured byfiltering with a filter having a pore diameter of 3 μm in the presentinvention. The content of the particles having a diameter of 3 μm ormore occupied in the whole solid in the polishing slurry in the presentinvention needs to be 500 ppm or less at a weight ratio, and, therefore,the scratch reduction effect is apparent. When the content of theparticles of 3 μm or more occupied in the whole solid is 200 ppm orless, it is more preferable since the scratch reduction effect islarger. When the content of the particles of 3 μm or more occupied inthe whole solid is 100 ppm or less, it is still more preferable sincethe scratch reduction effect is largest.

The content of the coarse particles of 3 μm or more can be calculated bythe weight measurement of the particles captured by filtering with afilter having a pore diameter of 3 μm. After the polishing slurry isseparately dried, the content of the whole solid in the polishing slurryis measured. For example, the weight of the remainder obtained by dryingthe polishing slurry of 10 g at 150° C. for 1 hour is measured to obtainthe solid concentration. The mass of the polishing slurry used forfiltering with a filter having a pore diameter of 3 μm is multiplied bythe solid concentration, and thereby the content of the whole solid canbe obtained. The filter having a pore diameter of 3 μm is preferably afilm (one layer) type filter for analysis on which a hole is formed bylaser processing. FIG. 1 shows an example of the surface magnifiedphotograph of such a filter. Examples of commercial items include acyclopore track etched membrane filter manufactured by Whatman. Sincethe pore size of such a filter for analysis is precise and thedistribution is also uniform, the particles can be exactly separated bythe particle size. It is suitable for observing the particles capturedon the filter using an optical microscope or an electron microscope.

Examples of means for reducing the content of the coarse particlesinclude filtration and classification, and are not limited thereto. Afilter for mass production is preferable for the filtration for reducingthe coarse particles. The filter for mass production has a multilayerstructure. The area and the life can be increased by reducing thediameter of the holes continuously from the outside of the filter to theinside, and a great amount of polishing slurries can be filtered.However, the hole is formed by not the laser machining but thesuperposed filter fibers. Though the captured particle diameter can bechanged by changing the diameter and density of the fiber, the fibersare not mutually fixed. Therefore, the hole may be enlarged, andparticles may fall out so that the exact separation of the particles bythe particle diameter is difficult. Therefore, even if the polishingslurry is passed through the filter for mass production having a porediameter smaller than 3 μm, particles of 3 μm or more may be capturedwhen the polishing slurry is then filtered through the filter foranalysis having a pore diameter of 3 μm.

For example, the content of the coarse particles can be reduced byfiltering multiple times through such a filter for mass production or byreducing the pore diameter of the filter for mass production.

The polymer additive agent for further improving flatness anddispersibility can be added to the polishing slurry. Though the polymeradditive agent is not limited to the following ones, for example,polymers such as an acrylic ester derivative, acrylic acid and acrylicacid salt can be added. Though the addition amount of the polymeradditive agent is not particularly limited, the addition amount ispreferably within the range of 5 parts to 20 parts by weight to thecerium oxide particle of 100 parts by weight. The weight-averagemolecular weight of the polymer additive agent is preferably within therange of 100 to 50,000, and more preferably 1,000 to 10,000. When themolecular weight is less than 100, sufficient polish speed is hardlyobtained at the time of polishing the silicon oxide film or a siliconnitride film. When the molecular weight exceeds 50,000, the dispersingagent has high viscosity, and the preservation stability of thepolishing slurry tends to be descended.

The pH of the polishing slurry is preferably within the range of 3 to 9,and more preferably 5 to 8. When the pH is smaller than 3, the chemicaloperation force is reduced, and the polish speed tends to be decreased.When the pH is larger than 9, the chemical operation is too strong, andthe surface to be polished may be dissolved in a shape of a dish(dishing). The pH was measured by a pH meter (for example, Model PH81,manufactured by YOKOGAWA ELECTRIC CORP.). After two-point calibratingusing a standard buffer solution (a phthalic-acid salt pH buffersolution pH: 4.21 (25° C.), neutral phosphoric acid salt pH buffersolution pH 6.86 (25° C.)), an electrode is put into a polishing slurry,and the value after 2 minutes or more and being stabilized can bemeasured.

The polishing slurry of the present invention can be prepared as asingle-liquid type polishing slurry comprising, for example, the ceriumoxide particles, the dispersing agent, the polymer additive agent andwater, and can also be prepared as a double-liquid type polishing slurrydividing a cerium oxide slurry comprising the cerium oxide particles,the dispersing agent and the water, and an adding liquid comprising thepolymer additive agent and the water. In each case, the stabilizedcharacteristic can be obtained.

When stored as double-liquid type polishing slurry dividing the ceriumoxide slurry and the adding liquid, the planarization characteristic andpolish speed can be adjusted by the arbitrary changeable combination ofthese two liquids. In the case of the double-liquid type, a method(immediately preceding mixture method) for sending the adding liquid andthe cerium oxide slurry at an arbitrary flux by separate piping, andjoining these pipings, that is, mixing both the adding liquid and thecerium oxide slurry just before a supplying piping outlet to supply on apolish plate, or a method (previous mixture method) for mixing both theadding liquid and the cerium oxide slurry at an arbitrary ratepreviously in a container and supplying is employed.

The polishing slurry of the present invention can be used for polishpressing a substrate against a polish cloth and pressurizing whilesupplying polish liquid between a film to be polished formed on thesubstrate and a polish cloth, and moving the polish cloth and the filmto be polished relatively to polish the film to be even.

Examples of the substrates include a substrate for the formation processof a semiconductor device such as a substrate in which an inorganicinsulating layer is formed on a semiconductor substrate of a stage wherea circuit element and

-   -   a wiring pattern are formed, or a semiconductor substrate of a        stage where a circuit element is formed or the like. Examples of        films to be polished include the inorganic insulating layer, for        example, a silicon oxide film layer, and a silicon nitride film        layer and an silicon oxide film layer.

EXAMPLE 1

Hereinafter, though the present invention is specifically described withreference to examples, the present invention is not limited thereto.

Commercially available cerium carbonate of about 6 kg was put into analumina container, and yellowish white powder of about 3 kg was obtainedby firing the cerium carbonate at 800° C. in air for 2 hours. The powderwas identified by an X-ray diffraction method, and was confirmed to becerium oxide. The particle diameter of the fired powder was within therange of 30 to 100 μm. Furthermore, the obtained cerium oxide powder of3 kg was dry grinded by using the jet mill to obtain the cerium oxideparticles.

Cerium oxide particles of 1000 g produced above, an aqueous solution ofammonium polyacrylate of 80 g (40% by weight), and deionized water of3920 g were mixed, and an ultrasonic distribution was performed for 10minutes while the mixture was stirred. The obtained dispersion liquidwas left and settled out at room temperature for 20 hours, and asupernatant fluid was obtained. After filtering the supernatant fluidthrough a filter for mass production having a pore diameter of 1.0 μm(filter fibers are mutually superposed to form a pore), the supernatantfluid was filtered through the filter for mass production having a porediameter of 1.0 μm again, and the solid content concentration wasadjusted to 5% by adding deionized water to produce a polishing slurryfor semiconductor planarization.

Referring to the particle diameter of the obtained polishing slurry forsemiconductor planarization, the undiluted the polishing slurry forsemiconductor planarization was measured on the conditions of arefractive-index of 1.9285, a light source of He—Ne laser, andabsorption 0 by using a laser diffraction type particle sizedistribution meter (manufactured by Malvern Instruments Ltd., tradename: Mastersizer Microplus). As a result, the median (D50) of thesecondary particle diameters was 190 nm, and the D99 was 0.7 μm. In thismeasurement, the particles having a diameter of 3 μm or more were notdetected.

The polishing slurry for semiconductor planarization obtained wasdiluted by 15 times so as to investigate the content of the coarseparticles, and the diluted polishing slurry of 30 g was filtered througha filter having a pore diameter of 3 μm (a cyclopore track etchedmembrane filter, manufactured by Whatman). The filter was dried at roomtemperature after filtration, and the weight of the filter was measured.The amount of coarse particles of 3 μm or more was calculated from aincrement in weight before and after filtration. The polishing slurry of10 g was separately dried at 150° C. for 1 hour, and the solidconcentration in the polishing slurry was calculated. As a result, theamount (weight ratio) of the coarse particles of 3 μm or more was 450ppm in the solid.

The above polishing slurry for semiconductor planarization was dilutedby 5 times with deionized water, and polish was performed by thefollowing method. The polish speed was 650 nm/min. When the wafersurface was observed by an optical microscope, 20 scratches wereobserved on the whole surface of the wafer of 200 mm.

[Polish Test Method]

Polish Load: 30 kPa

Polish Pad: foamed polyurethane resin, manufactured by Rodel Inc.(IC-1000)

Number of Rotations: polish plate of 75 rpm, pad of 75 rpm,

Polishing slurry Supply Rate: 200 mL/min,

Polish Object: P-TEOS deposition Si wafer (200 mm)

EXAMPLE 2

The cerium oxide particles of 1000 g produced in Example 1, an aqueoussolution of ammonium polyacrylate of 80 g (40% by weight), and deionizedwater of 3920 g were mixed, and an ultrasonic distribution was performedfor 10 minutes while the mixture was stirred. The obtained dispersionliquid was left and settled out at room temperature for 100 hours, and asupernatant fluid was obtained. After filtering the supernatant fluidthrough the filter for mass production having the pore diameter of 0.7μm, it was filtered through the filter for mass production having thepore diameter of 0.7 μm again, and the solid content concentration wasadjusted to 5% by adding deionized water to produce a polishing slurryfor semiconductor planarization.

The particle diameter of the obtained polishing slurry for semiconductorplanarization was measured in the same manner as Example 1. As a result,the median (D50) of the secondary particle diameters was 160 nm, and theD99 was 0.5 μm. The particles having a diameter of 3 μm or more were notdetected.

So as to investigate the content of the coarse particles, the amount ofcoarse particles of 3 μm or more was calculated in the same manner asExample 1 from an increment in weight before and after filtering theobtained polishing slurry for semiconductor planarization. As a result,the amount of the coarse particles of 3 μm or more was 50 ppm in thesolid.

The above polishing slurry for semiconductor planarization was dilutedby 5 times with deionized water, and polish was performed by the samepolish test method as that of Example 1. The polish speed was 350nm/min. When the surface of the wafer was observed by an opticalmicroscope, 10 scratches were observed on the whole surface of the waferof 200 mm.

COMPARATIVE EXAMPLE 1

The cerium oxide particles of 1000 g produced by the same method as inExample 1, and an aqueous solution of ammonium polyacrylate of 80 g (40%by weight), and deionized water of 3920 g were mixed, and an ultrasonicdistribution was performed for 10 minutes while the mixture was stirred.The obtained dispersion liquid was left and settled out at roomtemperature for 4 hours, and a supernatant fluid was obtained. Afterfiltering the supernatant fluid through the filter for mass productionhaving the pore diameter of 10 μm, the solid content concentration wasadjusted to 5% by adding the deionized water to produce a polishingslurry for semiconductor planarization.

The particle diameter of the obtained polishing slurry for semiconductorplanarization was measured in the same manner as in Example 1. As aresult, the median (D50) of the secondary particle diameters was 240 nm,and the D99 was 2.5 μm. The particles having a diameter of 3 μm or morewere not detected.

So as to investigate the content of the coarse particles, the amount ofcoarse particles of 3 μm or more was calculated in the same manner as inExample 1 from the increment in weight before and after filtering theobtained polishing slurry for semiconductor planarization. As a result,the amount of the coarse particles of 3 μm or more was 1200 ppm in thesolid.

The above polishing slurry for semiconductor planarization was dilutedby 5 times with deionized water, and polish was performed by the samepolish test method as that of Example 1. The polish speed was 700nm/min. When the wafer surface was observed by an optical microscope,100 scratches were observed on the whole surface of the wafer of 200 mm.

COMPARATIVE EXAMPLE 2

The cerium oxide particles of 1000 g produced by the same method as inExample 1, and an aqueous solution of ammonium polyacrylate of 80 g (40%by weight), and deionized water of 3920 g were mixed, and an ultrasonicdistribution was performed for 10 minutes while the mixture was stirred.The obtained dispersion liquid was left and settled out at roomtemperature for 4 hours, and the supernatant fluid was obtained. Thesolid content concentration was adjusted to 5% by adding deionized waterto the supernatant fluid to produce a polishing slurry for semiconductorplanarization.

The particle diameter of the obtained polishing slurry for semiconductorplanarization was measured in the same manner as in Example 1. As aresult, the median (D50) of the secondary particle diameters was 240 nm,and the D99 was 2.5 μm.

So as to investigate the content of the coarse particles, the amount ofcoarse particles of 3 μm or more was calculated in the same manner as inExample 1 from the increment in weight before and after filtering theobtained polishing slurry for semiconductor planarization. As a result,the amount of the coarse particles of 3 μm or more was 2500 ppm in thesolid.

The above polishing slurry for semiconductor planarization was dilutedby 5 times with deionized water, and polish was performed by the samepolish test method as Example 1. The polish speed was 700 nm/min. Whenthe wafer surface was observed by the optical microscope, 100 scratcheswere observed on the whole surface of the wafer of 200 mm.

According to Examples and Comparative Examples, the minor component of1200 ppm (0.12%) or less of Comparative Example 1 cannot be detected bythe laser diffraction type particle size distribution meter. On theother hand, even the minor component of 50 ppm of Example 2 can bedetected by a weight measuring method. From these results, the inventorconsiders that the weight measuring method has the higher measurementsensitivity for the coarse particles than the laser diffraction typeparticle size distribution meter.

INDUSTRIAL APPLICABILITY

The surface of the semiconductor in the wiring formation process can bepolished at a high speed by the present invention. Also, the surface ofthe semiconductor has good flatness, and scratches can be reduced.

1. A polishing slurry for semiconductor planarization containing ceriumoxide particles and water, wherein the content of the cerium oxideparticles having a diameter of at least 3 μm is not more than 500 ppm ina solid.
 2. The polishing slurry for semiconductor planarizationaccording to claim 1, further containing a dispersing agent.
 3. Thepolishing slurry for semiconductor planarization according to claim 1 or2, wherein the particle diameter is not more than 1 μm in 99% by volumeof the whole cerium oxide particles.